This invention relates to an apparatus for controlling an Exhaust Gas Recirculation (hereinafter referred to as EGR) valve which is disposed in an exhaust gas recirculation system.
FIG. 1 is a schematic arrangement diagram in which a control valve 11 serving as an EGR valve is disposed in an exhaust gas recirculation passage c which communicates an exhaust passage xe2x80x9caxe2x80x9d of an engine E and an intake passage b together. In such an apparatus for controlling the EGR valve, the driving of a direct current (DC) motor (hereinafter referred to as electric motor M) is controlled by an engine controller unit (hereinafter referred to as ECU) 51. The opening and closing of the control valve 11 is controlled by the electric motor M. By controlling the electric motor M, the opening degree of the control valve 11 can be adjusted.
Incidentally, in the conventional apparatus for controlling the EGR valve, a predetermined return torque is given to the control valve 11 in the valve-closing direction by an urging means, and a motor torque to vary the control valve 11 in the valve-opening direction is given by the driving of the electric motor M in the valve-opening direction. The control valve 11 is thus opened and closed by the balance of these torque.
As this kind of control apparatus, a description is made for example in JP-A 11-159405(1999) about an arrangement which is provided with: an open loop control system which controls the above-described electric motor M in an open loop manner so as to generate a motor torque depending on a target opening-closing position of the above-described control valve 11; and a feedback control system which controls the electric motor M in a feedback manner based on a deviation between input data corresponding to a targeted opening-closing position of the control valve 11 and detected data of the present opening-closing position of the control valve 11.
A description is first given of the driving method using this electric motor M. In case the opening degree of the control valve 11 is feedback-controlled by the electric motor M, the generated torque of the electric motor M is continuously controlled by feeding back the opening degree of the control valve 11 through continuous detection thereof with a position sensor such as of a sliding resistor type. Thus, the resolution of the adjusting opening degree of the control valve 11 can be infinitely minimized in theory.
The apparatus for controlling the EGR valve using this kind of electric motor M employs a so-called torque balance system. By a spring as an urging means, a predetermined return torque in the valve-closing direction is given and, by driving the electric motor M in the valve-opening direction, a variable motor torque in the valve-opening direction is given. Based on these torque balance, the valve-opening position is determined.
In this kind of control apparatus, since the EGR valve is constantly given the return torque, the opening-closing position (shift amount) varies with the inclination of lines A, B having a hysteresis due to friction as shown in FIG. 2.
Here, line A represents an operating characteristic at the time of opening the control valve 11 by increasing the motor torque, and line B represents an operating characteristic at the time of closing the control valve 11 by decreasing the motor torque. Depending on the spring constant of the spring to give the return torque, the inclination of the operating characteristics A, B change and, depending on the magnitude of the set torque, the operating characteristics A, B shift to right and left in FIG. 2.
Now, in order to control the control valve 11 with this kind of operating characteristics, suppose that there is employed a method in which the electric motor M is subject to a proportional (P) integral (I) control based on a deviation between the input data corresponding to the target opening-closing position of the control valve 11 and the detected data of the present opening-closing position of the control valve. In this case, from the relationship of the operating characteristics A, B as shown in FIG. 2, it becomes difficult to stabilize the control valve 11 in the target opening position.
In other words, in order to open the control valve 11 to the target opening position by increasing the motor torque, the motor torque is increased in order to perform the control along the operating characteristic A in FIG. 2. In this kind of control, in case the valve-opening position has exceeded the target value under the influence of an inertia, interference, or the like, the driving direction is reversed. However, if the hysteresis is present, the movement will not be reversed immediately, but will give rise to a delay. Should the P gain and the I gain be set without considering the delay due to hysteresis, vibrations will occur as shown in FIG. 3. Therefore, if no correction is made to the hysteresis, the P gain and the I gain are restricted, resulting in impairing of the response.
Considering the above-described situation, a description is now given, with reference to FIGS. 4 and 5, about an apparatus for controlling the control valve 11 in a so-called torque balance drive system using the electric motor M. In FIG. 4, reference numeral 1 denotes a valve body having formed therein a passage which forms a part of an exhaust gas recirculation passage c interposed in a recirculation system of the exhaust gas. By an upward movement of the control valve 11 (as illustrated) to thereby contact a valve seat 12, the exhaust gas recirculation passage c is closed and, by a downward movement of the control valve 11 to thereby depart from the valve seat 12, the exhaust gas recirculation passage c is opened.
Reference numeral 2 denotes a motor case for housing therein an electric motor M. In the electric motor M, reference numeral 21 denotes a rotor around which is wound by a coil 22, and reference numeral 23 denotes a yoke provided with a magnet 24. The lower end portion of the rotor 21 is rotatably supported on the valve body 1 by a bearing 27.
Inside the rotor 21, there is threadedly engaged a motor shaft 31. The motor shaft 31 is prevented from relatively rotating by a guide bush 13 on the body 1. Therefore, it follows that the motor shaft 31 moves upward and downward depending on the amount of rotation of the rotor 21. A valve shaft 14 is provided in contact with the lower end of the motor shaft 31, and an intermediate portion of the valve shaft 14 is guided by a guide seal 15 and a guide plate 16 so as to be movable upward and downward. The control valve 11 is attached to the lower end of the valve shaft 14.
Reference numeral 17 denotes a guide seal cover. Between a spring sheet 18 mounted on the upper end of the valve shaft 14 and the guide plate 16, there is interposed a return spring 19 for urging the valve shaft 14 in an upward direction, i.e., for urging the control valve 11 in a valve-closing direction.
The control valve 11 constituted as described above is driven by a torque balance system as described above. In other words, the control valve 11 is given a predetermined return torque in the valve-closing direction of the control valve 11 by the return spring 19 serving as the urging means, and is also given a variable motor torque in the valve-opening direction by the driving of the electric motor M. By the balance of these torque, the open/close of the control valve 11 is controlled.
FIG. 5 is a circuit block diagram showing an engine controller unit (ECU) 51 which supplies the electric motor M with a driving signal. Reference numeral 50 denotes a control part in the form of a microcomputer which determines the driving force of the electric motor M. Reference numeral 52 denotes a battery. Reference numeral 53 denotes a motor driving force converting part which converts the output of the control part 50 for supplying to the electric motor M, and is made up of: a Zener diode 53a; a diode 53b for forcing the current flow to the electric motor M unidirectional; a field-effect transistor (FET) 53c; and an interface 53d which is provided between the control part 50 and the FET 53c. Reference numeral 56 denotes a regulator to ensure a driving voltage (5V) for the control part 50.
The control part 50 receives as inputs through interfaces 58, 59, respectively, a detected signal from an operating state amount sensor 57 mounted on each part of the vehicle such as a crank angle sensor or the like, as well as a detected signal from a position sensor 40. The position sensor 40 in this example is provided with a movable contact part 42 for moving on a resistor 41 to which is applied a constant voltage (5V) from a voltage supply part 60. By the movement of the movable contact part 42 caused by the rotation of the rotor 21, a voltage corresponding to the moving position of the motor shaft 31 is outputted, as a detected signal, from the movable contact part 42.
Further, the above-described motor driving force converting part 53 switches on and off the voltage to be applied to the electric motor M at a constant period. By a pulse-width modulation (PWM) signal depending on the ratio of on-time and off-time per a period (driving duty), the FET 53c is operated by switching, thereby controlling an average driving voltage to be applied to the electric motor M.
Since the conventional apparatus for controlling the EGR valve is constituted as described above, there is the following problem, i.e., in case the closing position of the control valve changes with the lapse of time due to wear of the control valve, the valve seat, or the like, the open position of the control valve and the rotor origin point of the electric motor deviate from each other, with the result that the valve-opening starting position with which the valve opening of the control valve is started changes and that the control valve can no longer be accurately controlled.
This invention has been made to solve the above and other problems and has an object of obtaining an apparatus for controlling an EGR valve in which the valve-opening starting position is accurately detected and the valve opening control is accurately performed.
Further, this invention has an object of obtaining an apparatus for controlling an EGR valve in which the motor shaft can be prevented, at the time of valve closing, from strongly striking a stopper which restricts the operating range of the electric motor.
An apparatus for controlling an exhaust gas recirculation (EGR) valve comprises: a valve shaft having an open-close valve; a return spring for urging the valve shaft in a valve-closing direction; an electric motor for driving in a valve-opening direction a motor shaft abutting the valve shaft; a position detecting sensor for detecting a position of the motor shaft; and a computing means for computing a valve-opening starting position based on a detected signal of the position detecting sensor which detects, through movement of the motor shaft back and forth in both the valve-opening direction and the valve-closing direction, related positions of the motor shaft and the valve shaft at the time of the movement.
According to this arrangement, it is possible to accurately detect the valve-opening starting position at which the valve starts to open, without requiring a complicated apparatus constitution, thereby enabling to accurately control the amount of opening the valve.
The apparatus for controlling an EGR valve according to this invention is characterized in that opening and closing operation of the open-close valve is repeated several times prior to an operation of detecting the valve-opening position.
According to this arrangement, the seating situation of the valve on the valve seat is improved. As a result, the detection of the valve-opening starting position is performed surely and accurately, whereby the amount of valve opening can be controlled more accurately.
The apparatus for controlling an EGR valve according to this invention further comprises an assisting spring for urging the motor shaft in a direction opposite to that of the return spring, the urging being made with a force smaller than that of the return spring.
According to this arrangement, the motor shaft pushed back by the urging force of the return spring at the time of closing the valve is prevented from being strongly striking a stopper which restricts the operating range of the electric motor, thereby preventing the motor shaft from being damaged. Further, the valve-opening position at which the valve starts to open is accurately detectable, whereby the amount of valve opening is accurately controllable.
The apparatus for controlling an EGR valve according to this invention is characterized in that the computing means: drives the electric motor, thereby opening the open-close valve by urging the valve shaft with the motor shaft; thereafter sequentially weakens the driving force of the electric motor so as to move the valve shaft in the valve-closing direction by an urging force of the return spring, thereby detecting a motor shaft position at the time of valve closing as a fully-closed position; further moves the motor shaft in a direction away from the valve shaft and thereafter moves the motor shaft once again in a direction to come into contact with the valve shaft, thereby detecting the contact position of the motor shaft with the valve shaft as a confirmation position; and if a deviation between the confirmation position and the fully-closed position falls within a tolerance (tolerable deviation), makes the fully-closed position as the valve-opening starting position.
According to this arrangement, the valve-opening starting position at which the valve starts to open can be accurately detected and, therefore, the amount of the valve opening can be accurately controlled.
The apparatus for controlling an EGR valve according to this invention is characterized in that the computing means: drives the electric motor, thereby opening the open-close valve by urging the valve shaft with the motor shaft; thereafter sequentially weakens the driving force of the electric motor so as to move the valve shaft in a valve-closing direction by an urging force of the return spring, thereby detecting the motor shaft position at the time of valve closing as a fully-closed position; further moves the motor shaft in a direction away from the valve shaft and thereafter moves the motor shaft once again in a direction to come into contact with the valve shaft, thereby detecting the contact position of the motor shaft with the valve shaft as a confirmation position; and if a deviation between the confirmation position and the fully-closed position falls outside a tolerable deviation, repeats the above-described operations once again to thereby detect whether the deviation between the confirmation position and the fully-closed position falls within the tolerable deviation.
According to this arrangement, the valve-opening starting position at which the valve starts to open can be accurately detected and, therefore, the amount of opening the valve can be accurately controlled.
The apparatus for controlling an EGR valve according to this invention is characterized in that the computing means: sequentially increases a driving force to be supplied to the electric motor in the valve-opening direction, thereby detecting a duty at which the driving force changes as a result of contact of the motor shaft with the valve shaft; opens the open-close valve by sequentially increasing the driving force of the electric motor and thereafter closes the open-close valve by sequentially decreasing the driving force of the electric motor, thereby detecting a duty at which the driving force changes as a result of departing of the motor shaft from the valve shaft; and if a deviation between this duty and the earlier detected duty falls within a tolerable deviation, makes that position of the motor shaft at which the earlier detected duty was detected as the valve-opening starting position.
According to this arrangement, the valve-opening starting position at which the valve starts to open can be accurately detected and, therefore, the amount of operating the valve opening can be accurately controlled.